Conventional bearings for rotating shafts are subject to wear, noise, vibration and thermal breakdown. Until recently, practical magnetic bearings were either a permanent magnetic or an electromagnetic type. Permanent magnet bearings were subject to inherent static instabilities and had to be stabilized in at least one degree of freedom by non-magnetic bearings. Electromagnetic bearings often required elaborate position sensors and electronics to achieve stability.
Prior art devices attempted to improve magnet bearings by using the material property known as superconductivity. In those devices, either the bearing member or the rotating member, or both, are confined in a Type I superconducting state in order to achieve a magnetic pressure between the members and thereby provide a degree of levitation. Type I superconductors exhibit perfect diamagnetism up to a critical applied field, at which point superconductivity is lost and the magnetization of the sample rises abruptly.
Recent advances in the art of superconductivity have resulted in new ceramic compositions which exhibit superconducting properties at higher temperatures. These new superconductors are known as Type II materials with higher critical fields. Type II superconductors enable magnetic flux to penetrate into its interior in clusters of flux lines, establishing circulating superconducting currents within the superconductor. They, in turn, generate substantial magnetic fields and exert a positional pinning effect on a magnet levitated over the surface of the superconductor.
An important advantage of levitated superconducting bearings is its ability to allow rotational speeds of 10's of thousands of rpm. However, stability of prior art devices was a problem in that the effect of gravity or other forces often caused the devices to fail to achieve the desired reliability.